The invention concerns a method for filling barrels, especially kegs, with liquids, in which at least one gas is dissolved, whereby the barrel is pre-stressed with a pre-stress gas before being filled with liquid, after which liquid is fed to the barrel by means of a filling valve of a filling station, connected to a feed line, and the pre-stress gas contained in the barrel is removed during the filling process, as well as a device to carry out this method.
Carbon dioxide-containing beverages such as beer only keep their CO.sub.2 in solution, if the partial pressure of the CO.sub.2 gas above the liquid is at least as high as the saturation pressure in the liquid. If the gas pressure above the liquid is below the saturation pressure, the liquid loses CO.sub.2 ; but if the gas pressure is substantially above this, there is a danger that additional CO.sub.2 will go into solution. The uptake of gas will depend on the differential pressure between the saturation pressure in the liquid and the partial pressure above the liquid, the time available for the gas exchange, which is generally the same as the filling time of the barrel, and the size of the gas exchange area, i.e., the liquid surface. The danger of a gas uptake during the filling is significantly increased because of turbulence in the liquid occurring during the filling process. However, the gas exchange between liquid and the overlying gas atmosphere concerns not only the CO.sub.2, but also other gases present in the gas atmosphere, especially oxygen, which is taken up by the liquid according to the same laws. Yet oxygen is a major factor of product quality in the case of liquids, which can be damaged by microorganisms or whose shelf life is endangered by oxidation of the liquid's components.
In order to get the product through a valve into the barrel, whether a bottle or a keg, a differential pressure between feed line and interior of the barrel is necessary. The magnitude of the differential pressure determines the inflow rate of the product. Usually, in order to avoid increases of surface due to turbulence, the product is filled with initially low speed, which is then slowly increased. For this, the barrel is pre-stressed with a gas pressure that is substantially higher than the saturation pressure of the gas dissolved in the liquid. The actual liquid being filled is also maintained at this pressure level by tanks or pumps and supplied to the filling machine. After the pre-stressing of the barrel to the pressure of the supplied liquid, a connection is established between barrel and product feed line. The filling of the barrel with product is made possible by controlled venting of the pre-stress gas present in the barrel In this process, the differential pressure which is built up determines the flow rate of the liquid. Moreover, it is known that the gas escape is throttled toward the end of the filling, which reduces the differential pressure between the interior of the barrel and the feed line. This has the effect of reducing the quantity of product filled per unit of time toward the end of the filling process, which enables a precise shutoff when reaching a set quantity. This known method is termed "back gas control". The advantage of this control method is that the gas pressure above the liquid is at all times above the saturation pressure of the product.
The pre-stress pressure to be established is found by trial and error. At the start of the filling, the product should lose CO.sub.2 through turbulence, which results in local underpressures. This produces a desirable artificial foam on the liquid surface, whose bubbles contain only the released CO.sub.2 and, thus, protect the product against contact with the oxygen-containing gas atmosphere above it. During the further filling, the turbulence vanishes and so do the local underpressures. During the remaining fill time, the product again takes up CO.sub.2. Thus, the trick is to achieve an equilibrium between loss and further uptake of CO.sub.2 as a function Of CO.sub.2 content, temperature, barrel size, and estimated filling time.
Apart from the fact that the barrel has to be pre-stressed far above the saturation pressure in the case of back gas control and venting has to be conducted in a controlled manner in order to achieve a controlled filling rate, the reduction in the filling rate during the last filling segment is a problem. At constant inlet pressure of the liquid, the flow velocity can only be reduced if the differential pressure is decreased. For this, in the known techniques, the gas escape is throttled (or shut off, in extreme cases) and one waits until the increasing liquid level has achieved a raising of the counterpressure to the desired value by compressing the remaining gas volume present in the barrel. This period of time can be considerable, especially in the case of beer barrels. Thus, a 50-liter keg usually has an inlet cross section DN21, a maximum filling rate of 2.5 l/sec. and a differential pressure of 0.8 bar. If the keg is filled with 35 liters, then 15 liters of gas space must be compressed by 0.7 bar to reduce the rate. This requires 15.times.0.7=10.5 liters of liquid and (given the reducing rate of filling) around 8 seconds of filling time. Thus, a fast, accurate control is not possible, especially with possible fluctuation in feed pressures. Even more critical is the situation when not just one gas (for example, CO.sub.2), but two gases (for example, CO.sub.2 and N.sub.2) are deliberately dissolved in the product. N.sub.2 is added to beer nowadays for its foam stabilizing action. The best example of this is stout beer, whose creamy, long-lasting foam is produced by the dissolved N.sub.2 released during tapping. But N.sub.2 and CO.sub.2 have completely different solubilities and saturation pressure curves. While CO.sub.2 goes easily into solution and can only be brought out of solution with difficulty, it is extremely hard to place N.sub.2 in solution at all, and very easy to take it out of solution with the smallest amount of turbulence. A balance between outgassing at the start of filling and recapture of lost gas during the filling is almost impossible to find in the case of 2-gas systems. The quality of the product being filled therefore fluctuates. One tries to compensate for this by maintaining the ratio of the gas atmosphere CO.sub.2 to N.sub.2 different than the proportion of the dissolved gases. But this compromise only holds for one temperature or one barrel size and only for one product feed pressure. Mastery of these many factors and their tolerances with a control technique is not possible.
Another drawback of back gas control is that the barrel needs to be pre-stressed far above the saturation pressure with gas, generally CO.sub.2, in order to accomplish a pressure drop, which still lies above the saturation pressure of the gas even during maximum lowering of the interior pressure during the filling process. Since the gas is then vented into the atmosphere, this results in increased consumption of the greenhouse gas CO.sub.2, in addition to energy consumption, Furthermore, the operating personnel are exposed to the high emission of CO.sub.2.
A process of this type is known from GB-A-2,116,530 in which the kegs are filled by means of a connecting fitting that faces downward, whereby the liquid flows in through the carbon dioxide valve of the connecting fitting and the expelled gas is led off through the pressure release valves. Once the beer finally flows over the upper edge of the ascending tube, the barrel is completely full. In order to permit filling of the beer into kegs such that this is accompanied by low turbulence and low foaming and, in particular, a feature is provided that filling is carried out in 3 phases, whereby a first predetermined volume of liquid is measured out in an Initial stage and then this is introduced slowly into the keg and then a second predetermined volume of liquid is measured out in the subsequent rapid filling phase and this is introduced rapidly into the keg, and a third predetermined volume of liquid is measured out in the concluding phase of filling the vessel completely and this is then slowly introduced into the keg. The volumes of liquid, which are introduced into the keg on each occasion, are ascertained by means of an inductive gauge in the liquid line and are forwarded to an electronic evaluation and switching system, within which the measured voltage is digitized and forwarded to a gauge which Is calibrated in "liters" and which indicates the total volume of the keg. The volumes, which are desired for the individual filling phases, can be prescribed by a target value adjusting unit. In order to achieve the different filling volumes in the individual filling phases, an additional filling line is hooked up in the rapid filling phase. Thus the basis of the known process is the provision of two limiting values for the volume, which are capable of parameterization, whereby one can switch between a large and a small filling line on reaching these limiting values, The throughflow rate in the product supply line is not regulated.
Thus, the object of the Invention is to make smooth filling possible and to reduce the consumption of the pre-stressing gas.
In accordance with the invention, this object is solved, In essence, by the feature that the pre-stressing gas In the barrel is pre-stressed merely to a partial pressure which corresponds approximately to the saturation pressure of one of the gases which is dissolved in the liquid, which is being introduced, and that the flow-flow rate In the product supply line is measured and is regulated directly by altering the flow volume of the product.
In contrast to the prior art, the initially slow flowing in of the product and the increase in the flow velocity at the end of filling is no longer regulated indirectly by modulating the internal pressure of the keg but, rather, direct regulation of the flow volume of the product takes place.
An essential advantage of this new process resides in the feature that one can dispense completely with the previously necessary Installation of sensors for the product pressure since these pressures are no longer determinant for producing the flow velocity. As a result, the use of these highly precise and sensitive sensors and their technical-measurement calibration adjustment are no longer required.
A container, which is filled with a counter-pressure gas, is capable of reacting only very sluggishly to product fluctuations by increasing or decreasing the pressure of the relatively large volume of gas by blocking or opening the gas outlet. The change In pressure depends on the slowly rising level of product in the barrel. In the case of the present invention, on the other hand, the flow rate of the product into the keg can be kept stable at the desired predetermined value, despite changing product or countergas pressures due to change in the flow cross section.
The first cold product entering the hot keg causes residual quantities of atmospheric sterile steam in the barrel to suddenly condense. The pressure-modulating methods used thus far were not able to control this pressure collapse fast enough. The new method solves this task without difficulties and guarantees a controlled slow inflow of product, which is the prerequisite for a careful filling.
In a further modification of the invention, various filling curves can be entered into a data-processing unit to account for certain barrel sizes, types of fittings, different product temperatures and/or certain propellant gas ratios. These curves are produced by algorithms which are calculated or empirically obtained and which automatically correlate the appropriate flow velocities with the mentioned barrel components or product conditions. Thus, new product/barrel combinations can organize and process optimized self-learning fill profiles in this system. The filling curves are the setpoint values used to regulate the product volume flow.
In a preferred embodiment of this concept of the invention, the filling curves can be graphically modified and adjusted during production, e.g., with graphic interaction systems.
The gas inside the barrel can then be forced out by the incoming product through a simple overflow valve. The costly control apparatus formerly customary is no longer required for this. In the case of liquids containing several dissolved gases, the optimal gas composition can be established inside the barrel, since the same pressure prevails inside the barrel throughout the entire time of the filling process. In the conventional back gas control, the fluctuating pressures inside the barrel during the filling process resulted in different gas exchange behavior and, thus, an influencing of product quality during the various filling phases. This is completely eliminated by the invention.
According to a preferred modification of the invention, the pre-stress pressure inside the barrel is adjusted according to the saturation pressure after the filling. The basis for this concept of the invention is the fact that beer kegs are steamed for sterilization prior to filling and the cold product is poured into the still hot barrel. Fifty liters of beer with a temperature of around 3.degree. C. are poured into an approximately 12 kg metal barrel with a temperature of 100.degree. C. A mixing and equalization temperature is produced, which increases the temperature of the product in the barrel by around 4.degree. C. relative to the feed temperature. This, of course, alters the saturation pressures of the dissolved gases, so that the value to be adjusted according to the invention must correspond to that of the product in the filled barrel. This issue never came up in the past, because the counterpressure was always considerably above the saturation pressure.
A device to carry out the above-described method with a filling station, which supplies product liquid to be filled into the barrel across a feed line and from which pre-stress gas escaping from the barrel is taken away through a return gas line, has, according to the invention, a flow meter at the filling station to determine the flow-through velocity in the feed line of the filling station and a controllable diaphragm to adjust the product volume flow. In this way, the volume flow at each filling station can be individually adjusted as a function of the filling quantity or filling level, absolutely independent of the feed pressure of the product being filled and independent of the other filling stations, which might be present at the filling machine. In many cases, furthermore, there is a simplification of the customary pressure tanks upstream from the filling machines and their controls, since these likewise can be adjusted to the optimal gas mixture corresponding to the relations at saturation pressure, without influencing the product.
The product volume flow is regulated by a controller on the basis of the flow velocity determined by the flow meter as the actual value and a filling curve as the setpoint value, preferably adjusted to the barrel size, type of fitting, product temperature and/or proportions of propellant gas in the product and stored in a data-processing unit. According to the invention, the diaphragm cross section is continuously adjustable for this.
According to a preferred embodiment of the invention, an overflow valve is provided in the return gas line, through which the return gas is taken away. Further modifications, advantages, and application possibilities of the invention will follow from the description of an example of embodiment and the drawing below.